The production of sulfones through reaction of 2,6-dialkyl phenol with a sulfonating agent is known. The product, however, generally suffers from low purity. Consequently, various steps have been employed to reduce contamination.
In, for example, U.S. Pat. No. 3,383,421 of Fox et al, there is claimed a process yielding bis(3,5-dialkyl-4-hydroxyphenyl) sulfone. That process involves:
(a) reaction of a 2,6-dialkyl phenol where each alkyl group has from 1 to 4 carbon atoms with sulfuric acid within a temperature range of 155.degree. to 170.degree. C. in the presence of an organic liquid capable of forming an azeotrope with the water of reaction, the azeotrope having a boiling point within the reaction temperature range; PA1 (b) recovering sulfone from the reaction mixture; PA1 (c) dissolving said sulfone in aqueous solution of caustic soda or ammonia; PA1 (d) neutralizing the aqueous solution with acid to pH ranging between 4 and 6; and PA1 (e) collecting the sulfone in the form of white crystals.
The disclosure of that patent emphasized the importance of steps (c) and (d) to product purity. In addition, however, additional measures intended to reduce formation of, or remove, contaminants are mentioned.
The presence of contaminant impurities in bis (3,5-dialkyl-4-hydroxyphenyl) sulfones raises special concerns. They include partial reaction products such as phenol sulfonic acids and by-products of reaction such as quinone type color bodies, sulfonic acid and derivatives and sulfonic isomers.
Impurities are most particularly objectionable for the recent newer usages of bis(3,5-dialkyl-4-hydroxyphenyl) sulfones as monomeric constituents. A representative such usage is described in U.S. Pat. No. 3,737,409 of Fox. There, such sulfones are employed in the production of carbonate polymers.
Whereas these impurities were often tolerable for such prior art utilities as plasticizers, wetting agents, agents for combating pests, auxiliary substances for use in canning, dyestuff and the like, they are very detrimental in the formation of high molecular weight polymers and copolymers. There they may additionally cause undesirable chain termination, branching and cross-linking as well as predispose the product to various degradation processes.
As a result of the foregoing drawbacks diphenyl sulfones of improved purity remain highly desirable.